Disruptive behavior disorders are characterized by antisocial, aggressive behaviors. Externalizing problems are the most commonly diagnosed mental health problems of childhood. They tend to be stable over time, resistant to treatment, and linked to psychiatric disorders in adolescence and adulthood. Early onset aggression is a precursor of life-course persistent antisocial behavior. Little is known, however, about constitutional and environmental factors, and their interactions, that contribute to different developmental outcomes. Eighty-two 4-5 year-old children at low, moderate or high risk for later disruptive behavior disorders (based on initial levels of externalizing problems), have been studied again at three subsequent time points; 6-7, 8-10, and 12-13 years. Social, emotional, cognitive, and physiological areas of child functioning are examined, in conjunction with socialization experiences. The goal is to identify key factors that contribute to continuity and change over time in young children's behavioral problems. Because antisocial, disruptive behaviors often are comorbid with anxiety and depression, the developmental trajectories for these internalizing problems also are investigated. Several child and parent risk and protective factors that contribute to continuity versus amelioration of problems during middle childhood were previously reported. The findings from three new projects are summarized next. The first two focus on the role of early child characteristics and parental environmental factors that influence the development of emotional and behavioral problems. The third examines the role of physiological reactivity in the expression of problems and psychiatric symptoms in early adolescence. (1) Parents' observed and self-reported socialization practices often are accurately reflected in children's and symbolic play. By early grade school, both disruptive girls and boys perceived parents as punitive more often than non-aggressive children. Antisocial girls (but not antisocial boys) also perceived more parental rejection and love withdrawal, indicating greater concerns about relationships with family members. These antisocial girls also were more likely to experience anxiety and mood symptoms by early adolescence, suggesting important links between socialization experiences and psychiatric outcomes.(2) Girls both at preschool and school age, expressed more submissive emotions (sadness and anxiety) than boys (as observed during and emotionally arousing family game interaction. Parents were more responsive to these emotions in girls than boys. Thus, in addition to the child's contribution, parents responsed in a way that would encourage gender-role consistent emotion expressions. These early observed emotions predicted psychiatric symptoms of depression two years later. This indicates the importance of early detailed observations of children's emotions expressed during family interactions and parental socialization of emotion for understanding the emergence of later psychiatric symptoms. (3) Self-reported emotional states, heart rate and blood pressure were examined before and after adolescents engaged in two socially challenging, evaluative manipulations. Internalizing problems were associated with greater anxiety and cardiovascular arousal, whereas externalizing problems predicted greater hostility but less cardiovascular arousal. These findings reflect the need to incorporate comorbid characteristics and multiple response systems into studies of the links between physiological reactivity to stress and emotional and behavioral problems.